Jay M. Tenenbaum became a multimillionaire in the Internet boom of the late 1990s. But it wasn’t until he was diagnosed with a lethal cancer that he found his calling as an Internet entrepreneur.

Dr. Tenenbaum learned in 1998 that he had melanoma, the most serious kind of skin cancer. He underwent surgery and took an experimental vaccine for a year. Then, nearly five years ago, the cancer returned, having spread to his liver. “That’s when I started looking at my mortality seriously,” says the 65-year-old from Portola Valley, Calif.

Frustrated with his treatment options, Dr. Tenenbaum began investigating other potential therapies. He found dozens of patient-advocacy organizations dedicated to melanoma that raised money and supported scientific research. They “all had good ideas,” he says, “but no one had put the different pieces together in the right way that would let them make progress in finding a drug in the lifetime of a patient.”